Contention window size adjustment in a wireless communication system

ABSTRACT

Apparatuses, methods, and systems are disclosed for contention window size adjustment. One apparatus includes a transmitter that transmits data on a carrier to a set of devices in a first transmission burst having a duration of at least one subframe. In some embodiments, the set of devices includes one or more devices. In various embodiments, the apparatus includes a receiver that receives feedback information from each device. In certain embodiments, the apparatus includes a processor that determines, based on the feedback information, whether interference above a predetermined level exists on the carrier during the first transmission burst at each device, adjusts a contention window size based on the determination of whether interference above the predetermined level exists on the carrier during the first transmission burst at each device, and determines a value N between a predetermined minimum contention window size and the adjusted contention window size.

FIELD

The subject matter disclosed herein relates generally to wirelesscommunications and more particularly relates to contention window sizeadjustment in a wireless communication system.

BACKGROUND

The following abbreviations are herewith defined, at least some of whichare referred to within the following description.

3GPP Third Generation Partnership Project

ACK Positive-Acknowledgment

BLER Block Error Ratio

BPSK Binary Phase Shift Keying

CAZAC Constant Amplitude Zero Auto Correction

CCA Clear Channel Assessment

CCE Control Channel Element

CP Cyclic Prefix

CQI Channel Quality Information

CSI Channel State Information

CSS Common Search Space

CWS Contention Window Size

DCI Downlink Control Information

DL Downlink

eCCA Enhanced Clear Channel Assessment

eNB Evolved Node B

EPDCCH Enhanced Physical Downlink Control Channel

ETSI European Telecommunications Standards Institute

FBE Frame Based Equipment

FDD Frequency Division Duplex

FDMA Frequency Division Multiple Access

FEC Forward Error Correction

HARQ Hybrid Automatic Repeat Request

LAA Licensed Assisted Access

LBE Load Based Equipment

LBT Listen-Before-Talk

LTE Long Term Evolution

MCL Minimum Coupling Loss

MCS Modulation and Coding Scheme

MU-MIMO Multi-User, Multiple-Input, Multiple-Output

NACK or NAK Negative-Acknowledgment

OFDM Orthogonal Frequency Division Multiplexing

PCell Primary Cell

PBCH Physical Broadcast Channel

PDCCH Physical Downlink Control Channel

PDSCH Physical Downlink Shared Channel

PHICH Physical Hybrid ARQ Indicator Channel

PRACH Physical Random Access Channel

PRB Physical Resource Block

PUCCH Physical Uplink Control Channel

PUSCH Physical Uplink Shared Channel

QoS Quality of Service

QPSK Quadrature Phase Shift Keying

RAR Random Access Response

RRC Radio Resource Control

RX Receive

SC-FDMA Single Carrier Frequency Division Multiple Access

SCell Secondary Cell

SCH Shared Channel

SIB System Information Block

SINR Signal-to-Interference-Plus-Noise Ratio

SR Scheduling Request

TBS Transport Block Size

TDD Time-Division Duplex

TDM Time Division Multiplex

TX Transmit

UCI Uplink Control Information

UE User Entity/Equipment (Mobile Terminal)

UL Uplink

UMTS Universal Mobile Telecommunications System

WiMAX Worldwide Interoperability for Microwave Access

In wireless communications networks, LAA facilitates an LTE system touse an unlicensed spectrum with assistance from licensed carrier. LAAfurther aims to facilitate the fair coexistence with other technologiesover the unlicensed spectrum and to satisfy various regulatoryrequirements in different countries and regions. As stated in LAA SI,TR36.889. an LBT procedure may facilitate fair and friendly coexistenceof LAA with other operators and technologies operating in the unlicensedspectrum. In TR36.889, various LBT schemes are defined, including acategory 4 relating to LBT with random back-off with a contention windowof variable size. Specifically, TR36.889 states for category 4 that“[t]he LBT procedure has the following as one of its components. Thetransmitting entity draws a random number N within a contention window.The size of contention window is specified by the minimum and maximumvalue of N. The transmitting entity can vary the size of the contentionwindow before drawing the random number N. The random number N is usedin the LBT procedure to determine the duration of time that the channelis sensed to be idle before the transmitting entity transmits on thechannel.”

In certain configurations, a contention window size (“CWS”)may beupdated after the completion of each downlink transmission burst. Inother configurations, the CWS for LBT category 4 channel access schemein an unlicensed carrier may only be increased in situations with highload in order to avoid the channel collision or decreased in situationswith low load in order to improve spectrum efficiency. For each adaptiveadjustment, LAA base units (e.g., eNBs) may facilitate various equipmenthaving a fair share of unlicensed spectrum access opportunities (e.g.,for itself and for all the scheduled remote units (e.g., UEs)). In themeantime, base units may also aim to adjust the CWS to increase theoverall unlicensed spectrum utilization efficiency and reduce theprobability of transmission collision.

There are various different interference situations involving base unitsand remote units. In some situations, a base unit may encounter aproblem with hidden nodes. One example is shown in a wirelesscommunication system 700 illustrated in FIG. 7. The wirelesscommunication system 700 includes a base unit 702 (e.g., an LAA eNB)having a CCA range 704 and a cell coverage area 706. The base unit 702transmits downlink data to its served remote unit 708 (e.g., UE1).Another node, which in this example is a Wi-Fi AP 710, is located nearbyto the remote unit 708, but the Wi-Fi AP 710 transmissions cannot besensed by the base unit 702. In this case, for DL PDSCH transmission tothe remote unit 708, the CWS may benefit from being increased to avoidpossible collision with Wi-Fi transmission. However, given that the baseunit 702 is unable to detect the presence of the Wi-Fi AP 710 based onthe CCA energy detection or preamble detection due to coupling lossbetween the base unit 702 and the Wi-Fi AP 710, the base unit 702 mayactually decrease its CWS for fast channel access assuming.Consequently, transmission collision between the base unit 702 and theWi-Fi AP 710 may occur.

In another configuration, the CWS may be adjusted based on HARQ-ACKfeedback. A similar mechanism is used in Wi-Fi: if ACK is not receivedafter a frame from a station, a Wi-Fi AP determines that a collisionhappened and therefore doubles the CWS; otherwise, Wi-Fi AP resets theCWS to the minimum value. It is noted that in Wi-Fi, a transmissionburst is only for a single remote unit or station. On the other hand,for LAA, it is possible that a transmission burst may include datatransmitted to more than one remote unit. Therefore, this ACK/NACK basedtriggering mechanism has some drawbacks for LAA, especially in the casethat a base unit schedules multiple remote units in one DL transmissionburst or even schedules multiple remote units in one single subframe.ACK/NACK corresponding to each remote unit's DL data in each DL subframewill be reported to the base unit. Therefore, adapting the CWS based onthe HARQ-ACK from all scheduled remote units collectively may notreflect the remote unit-specific interference situations present toproperly adjust the CWS. One example is shown in a wirelesscommunication system 800 illustrated in FIG. 8. The wirelesscommunication system 800 includes a base unit 802 (e.g., an LAA eNB)having a CCA range 804 and a cell coverage area 806. The base unit 802transmits downlink data to its served remote units 808 (e.g., UE1) and810 (e.g., UE2). Another node, which in this example is a Wi-Fi AP 812,is located nearby to the remote unit 808, but the Wi-Fi AP 812transmissions cannot be sensed by the base unit 802 or the remote unit810. The remote unit 808 suffers the interference from the hidden nodeof Wi-Fi AP 812, while remote unit 810 has no hidden node problem.Therefore, serving remote units 808 and 810 may use different CWS foroptimal performance.

BRIEF SUMMARY

Apparatuses for contention window size adjustment are disclosed. Methodsand systems also perform the functions of the apparatus. In oneembodiment, the apparatus includes a transmitter that transmits data ona carrier to a set of devices in a first transmission burst having aduration of at least one subframe. In some embodiments, the set ofdevices includes one or more devices. In various embodiments, theapparatus includes a receiver that receives feedback information fromeach device of the set of devices. In certain embodiments, the apparatusincludes a processor that determines, based on the feedback information,whether interference above a predetermined level exists on the carrierduring the first transmission burst at each device of the set of devicesadjusts a contention window size based on the determination of whetherinterference above the predetermined level exists on the carrier duringthe first transmission burst at each device of the set of devices, anddetermines a value N between a predetermined minimum contention windowsize and the adjusted contention window size.

In one embodiment, the transmitter transmits a second transmission burston the carrier at least N time slots after the end of the firsttransmission burst, wherein the duration of each time slot ispredetermined. In a further embodiment, the feedback information fromeach device of the set of devices includes hybrid automatic repeatrequest acknowledgement (“HARQ-ACK”) feedback corresponding to the datatransmitted in the first transmission burst to the device. In someembodiments, the processor determines, based on the feedbackinformation, that interference above the predetermined level exists onthe carrier during the first transmission burst for a device of the setof devices if a percentage of negative-acknowledgments (“NAKs”) in theHARQ-ACK feedback from the device is greater than a predeterminedthreshold percentage. In certain embodiments, the processor determines,based on the feedback information, that interference above thepredetermined level exists on the carrier during the first transmissionburst for a device of the set of devices if more than a predeterminednumber of consecutive NAKs exist in the HARQ-ACK feedback from thedevice.

In another embodiment, the feedback information from each device of theset of devices includes channel quality information (“CQI”) feedbackfrom the device corresponding to the CQI of the device in the firsttransmission burst. In various embodiments, the processor determines,based on the feedback information, that interference above thepredetermined level exists on the carrier during the first transmissionburst for a device of the set of devices if the CQI feedback from thedevice is less than a latest CQI feedback from the device before thefirst transmission burst by a predetermined amount.

In some embodiments, adjusting the contention window size includesincreasing the contention window size if interference above thepredetermined level exists on the carrier during the first transmissionburst for more than a predetermined percentage of devices in the set ofdevices. In various embodiments, adjusting the contention window sizeincludes decreasing the contention window size if interference above thepredetermined level exists on the carrier during the first transmissionburst for less than a predetermined percentage of devices in the set ofdevices. In one embodiment, adjusting the contention window sizeincludes increasing the contention window size if data is to betransmitted in the second transmission burst to at least one devicehaving interference above the predetermined level on the carrier duringthe first transmission burst. In certain embodiments, adjusting thecontention window size includes decreasing the contention window size ifdata is not to be transmitted in the second transmission burst to anydevice having interference above the predetermined level on the carrierduring the first transmission burst.

A method for contention window size adjustment, in one embodiment,includes transmitting data on a carrier to a set of devices in a firsttransmission burst having a duration of at least one subframe. In suchan embodiment, the set of devices may include one or more devices. Invarious embodiments, the method may include receiving feedbackinformation from each device of the set of devices. In some embodiments,the method includes determining, based on the feedback information,whether interference above a predetermined level exists on the carrierduring the first transmission burst at each device of the set ofdevices. In a further embodiment, the method includes adjusting acontention window size based on the determination of whetherinterference above the predetermined level exists on the carrier duringthe first transmission burst at each device of the set of devices. Invarious embodiments, the method includes determining a value N between apredetermined minimum contention window size and the adjusted contentionwindow size.

In certain embodiments, the method includes transmitting a secondtransmission burst on the carrier at least N time slots after the end ofthe first transmission burst, wherein the duration of each time slot ispredetermined. In one embodiment, the feedback information from eachdevice of the set of devices includes hybrid automatic repeat requestacknowledgement (“HARQ-ACK”) feedback corresponding to the datatransmitted in the first transmission burst to the device. In certainembodiments, determining, based on the feedback information, whetherinterference above the predetermined level exists on the carrier duringthe first transmission burst at each device of the set of devicesincludes determining, based on the feedback information, thatinterference above the predetermined level exists on the carrier duringthe first transmission burst for a device of the set of devices if apercentage of negative-acknowledgments (“NAKs”) in the HARQ-ACK feedbackfrom the device is greater than a predetermined threshold percentage.

In some embodiments, determining, based on the feedback information,whether interference above the predetermined level exists on the carrierduring the first transmission burst at each device of the set of devicesincludes determining, based on the feedback information, thatinterference above the predetermined level exists on the carrier duringthe first transmission burst for a device of the set of devices if morethan a predetermined number of consecutive NAKs exist in the HARQ-ACKfeedback from the device. In one embodiment, the feedback informationfrom each device of the set of devices includes channel qualityinformation (“CQI”) feedback from the device corresponding to the CQI ofthe device in the first transmission burst.

In one embodiment, determining, based on the feedback information,whether interference above the predetermined level exists on the carrierduring the first transmission burst at each device of the set of devicesincludes determining, based on the feedback information, thatinterference above the predetermined level exists on the carrier duringthe first transmission burst for a device of the set of devices if theCQI feedback from the device is less than a latest CQI feedback from thedevice before the first transmission burst by a predetermined amount.

In certain embodiments, adjusting the contention window size includesincreasing the contention window size if interference above thepredetermined level exists on the carrier during the first transmissionburst for more than a predetermined percentage of devices in the set ofdevices. In various embodiments, adjusting the contention window sizeincludes decreasing the contention window size if interference above thepredetermined level exists on the carrier during the first transmissionburst for less than a predetermined percentage of devices in the set ofdevices.

In various embodiments, adjusting the contention window size includesincreasing the contention window size if data is to be transmitted inthe second transmission burst to at least one device having interferenceabove the predetermined level on the carrier during the firsttransmission burst. In one embodiment, adjusting the contention windowsize includes decreasing the contention window size if data is not to betransmitted in the second transmission burst to any device havinginterference above the predetermined level on the carrier during thefirst transmission burst.

In one embodiment, an apparatus includes a receiver that receives dataon a carrier in a transmission burst with a duration of at least onesubframe. In various embodiments, the apparatus may include a processorthat determines an indication of whether interference above apredetermined level exists on the carrier during the transmission burstby comparing a received signal-to-interference-plus-noise ratio (“SINR”)in a subframe in the transmission burst with a SINR that achieves apredetermined target block error ratio (“BLER”) for an indicatedmodulation and coding scheme for the data transmitted in the subframe.The apparatus may also include a transmitter that transmits theindication to a device.

Another method for contention window size adjustment, in one embodiment,includes receiving data on a carrier in a transmission burst with aduration of at least one subframe. In various embodiments, the methodincludes determining an indication of whether interference above apredetermined level exists on the carrier during the transmission burstby comparing a received signal-to-interference-plus-noise ratio (“SINR”)in a subframe in the transmission burst with a SINR that achieves apredetermined target block error ratio (“BLER”) for an indicatedmodulation and coding scheme for the data transmitted in the subframe.In some embodiments, the method includes transmitting the indication toa device.

BRIEF DESCRIPTION OF THE DRAWINGS

A more particular description of the embodiments briefly described abovewill be rendered by reference to specific embodiments that areillustrated in the appended drawings. Understanding that these drawingsdepict only some embodiments and are not therefore to be considered tobe limiting of scope, the embodiments will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings, in which:

FIG. 1 is a schematic block diagram illustrating one embodiment of awireless communication system for contention window size adjustment;

FIG. 2 is a schematic block diagram illustrating one embodiment of anapparatus that may be used for contention window size adjustment;

FIG. 3 is a schematic block diagram illustrating another embodiment ofan apparatus that may be used for contention window size adjustment;

FIG. 4 illustrates one embodiment of communication used for contentionwindow size adjustment;

FIG. 5 is a schematic flow chart diagram illustrating one embodiment ofa method for contention window size adjustment;

FIG. 6 is a schematic flow chart diagram illustrating another embodimentof a method for contention window size adjustment;

FIG. 7 is a schematic block diagram illustrating one embodiment of awireless communication system that may use contention window sizeadjustment; and

FIG. 8 is a schematic block diagram illustrating another embodiment of awireless communication system that may use contention window sizeadjustment.

DETAILED DESCRIPTION

As will be appreciated by one skilled in the art, aspects of theembodiments may be embodied as a system, apparatus, method, or programproduct. Accordingly, embodiments may take the form of an entirelyhardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.” Furthermore,embodiments may take the form of a program product embodied in one ormore computer readable storage devices storing machine readable code,computer readable code, and/or program code, referred hereafter as code.The storage devices may be tangible, non-transitory, and/ornon-transmission. The storage devices may not embody signals. In acertain embodiment, the storage devices only employ signals foraccessing code.

Certain of the functional units described in this specification tray belabeled as modules, in order to more particularly emphasize theirimplementation independence. For example, a module may be implemented asa hardware circuit comprising custom very-large-scale integration(“VLSI”) circuits or gate arrays, off-the-shelf semiconductors such aslogic chips, transistors, or other discrete components. A module mayalso be implemented in programmable hardware devices such as fieldprogrammable gate arrays, programmable array logic, programmable logicdevices or the like.

Modules may also be implemented in code and/or software for execution byvarious types of processors. An identified module of code may, forinstance, include one or more physical or logical blocks of executablecode which may, for instance, be organized as an object, procedure, orfunction. Nevertheless, the executables of an identified module need notbe physically located together, but may include disparate instructionsstored in different locations which, when joined logically together,include the module and achieve the stated purpose for the module.

Indeed, a module of code may be a single instruction, or manyinstructions, and may even be distributed over several different codesegments, among different programs, and across several memory devices.Similarly, operational data may be identified and illustrated hereinwithin modules, and may be embodied in any suitable form and organizedwithin any suitable type of data structure. The operational data may becollected as a single data set, or may be distributed over differentlocations including over different computer readable storage devices.Where a module or portions of a module are implemented in software, thesoftware portions are stored on one or more computer readable storagedevices.

Any combination of one or more computer readable medium may be utilized.The computer readable medium may be a computer readable storage medium.The computer readable storage medium may be a storage device storing thecode. The storage device may be, for example, but not limited to, anelectronic, magnetic, optical, electromagnetic, infrared, holographic,micromechanical, or semiconductor system, apparatus, or device, or anysuitable combination of the foregoing.

More specific examples (a non-exhaustive list) of the storage devicewould include the following: an electrical connection having one or morewires, a portable computer diskette, a hard disk, a random access memory(“RAM”), a read-only memory (“ROM”), an erasable programmable read-onlymemory (“EPROM” or Flash memory), a portable compact disc read-onlymemory (“CD-ROM”), an optical storage device, a magnetic storage device,or any suitable combination of the foregoing. In the context of thisdocument, a computer readable storage medium may be any tangible mediumthat can contain, or store a program for use by or in connection with aninstruction execution system, apparatus, or device.

Code for carrying out operations for embodiments may be any number oflines and may be written in any combination of one or mote programminglanguages including an object oriented programming language such asPython, Ruby, Java, Smalltalk, C++, or the like, and conventionalprocedural programming languages, such as the “C” programming language,or the like, and/or machine languages such as assembly languages. Thecode may execute entirely on the user's computer, partly on the user'scomputer, as a stand-alone software package, partly on the user'scomputer and partly on a remote computer or entirely on the remotecomputer or server. In the latter scenario, the remote computer may beconnected to the user's computer through any type of network, includinga local area network (“LAN”) or a wide area network (“WAN”), or theconnection may be made to an external computer (for example, through theInternet using an Internet Service Provider).

Reference throughout this specification to “one embodiment,” “anembodiment,”or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment. Thus, appearances of the phrases“in one embodiment,” “in an embodiment,” and similar language throughoutthis specification may, but do not necessarily, all refer to the sameembodiment, but mean “one or more but not all embodiments” unlessexpressly specified otherwise. The terms “including,”“comprising”“having,” and variations thereof mean “including but not limited to,”unless expressly specified otherwise. An enumerated listing of itemsdoes not imply that any or all of the items are mutually exclusive,unless expressly specified otherwise. The terms “a,” “an,” and “the”also refer to “one or more” unless expressly specified otherwise.

Furthermore, the described features, structures, or characteristics ofthe embodiments may be combined in any suitable manner. In the followingdescription, numerous specific details are provided, such as examples ofprogramming, software modules, user selections, network transactions,database queries, database structures, hardware modules, hardwarecircuits, hardware chips, etc., to provide a thorough understanding ofembodiments. One skilled in the relevant art will recognize, however,that embodiments may be practiced without one or more of the specificdetails, or with other methods, components, materials, and so forth. Inother instances, well-known structures, materials, or operations are notshown or described in detail to avoid obscuring aspects of anembodiment.

Aspects of the embodiments are described below with reference toschematic flowchart diagrams and/or schematic block diagrams of methods,apparatuses, systems, and program products according to embodiments. Itwill be understood that each block of the schematic flowchart diagramsand/or schematic block diagrams, and combinations of blocks in theschematic flow chart diagrams and/or schematic block diagrams, can beimplemented by code. These code may be provided to a processor of ageneral purpose computer, special purpose computer, or otherprogrammable data processing apparatus to produce a machine, such thatthe instructions, which execute via the processor of the computer orother programmable data processing apparatus, create means forimplementing live functions/acts specified in the schematic flowchartdiagrams and/or schematic block diagrams block or blocks.

The code may also be stored in a storage device that can direct acomputer, other programmable data processing apparatus, or other devicesto function in a particular manner, such that the instructions stored inthe storage device produce an article of manufacture includinginstructions which implement the function/act specified in the schematicflowchart diagrams and/or schematic block diagrams block or blocks.

The code may also be loaded onto a computer, other programmable dataprocessing apparatus, or other devices to cause a series of operationalsteps to be performed on the computer, other programmable apparatus orother devices to produce a computer implemented process such that thecode which execute on the computer or other programmable apparatusprovide processes for implementing the functions/acts specified in theflowchart and/or block diagram block or blocks.

The schematic flowchart diagrams and/or schematic block diagrams in theFigures illustrate the architecture, functionality, and operation ofpossible implementations of apparatuses, systems, methods and programproducts according to various embodiments. In this regard, each block inthe schematic flowchart diagrams and/or schematic block diagrams mayrepresent a module, segment, or portion of code, which includes one ormore executable instructions of the code for implementing the specifiedlogical function(s).

It should also be noted that, in some alternative implementations, thefunctions noted in the block may occur out of the order noted in theFigures. For example, two blocks shown in succession may, in fact, beexecuted substantially concurrently, or the blocks may sometimes beexecuted in the reverse order, depending upon the functionalityinvolved. Other steps and methods may be conceived that are equivalentin function, logic, or effect to one or more blocks, or portionsthereof, of the illustrated Figures.

Although various arrow types and line types may be employed in theflowchart and/or block diagrams, they are understood not to limit thescope of the corresponding embodiments. Indeed, some arrows or otherconnectors may be used to indicate only the logical flow of the depictedembodiment. For instance, an arrow may indicate a waiting or monitoringperiod of unspecified duration between enumerated steps of the depictedembodiment. It will also be noted that each block of the block diagramsand/or flowchart diagrams, and combinations of blocks in the blockdiagrams and/or flowchart diagrams, can be implemented by specialpurpose hardware-based systems that perform the specified functions oracts, or combinations of special purpose hardware and code.

The description of elements in each figure may refer to elements ofproceeding figures. Like numbers refer to like elements in all figures,including alternate embodiments of like elements.

FIG. 1 depicts an embodiment of a wireless communication system 100 forcontention window size adjustment. In one embodiment, the wirelesscommunication system 100 includes remote units 102, base units 104, andunlicensed carriers 106. Even though a specific number of remote units102, base units 104, and unlicensed carriers 106 are depicted in FIG. 1,one of skill in the art will recognize that any number of remote units102, base units 104, and unlicensed carriers 106 may be included in thewireless communication system 100.

In one embodiment, the remote units 102 may include computing devices,such as desktop computers, laptop computers, personal digital assistants(“PDAs”), tablet computers, smart phones, smart televisions (e.g.,televisions connected to the Internet), set-top boxes, game consoles,security systems (including security cameras), vehicle on-boardcomputers, network devices (e.g., routers, switches, modems), or thelike. In some embodiments, the remote units 102 include wearabledevices, such as smart watches, fitness bands, optical head-mounteddisplays, or the like. Moreover, the remote units 102 may be referred toas subscriber units, mobiles, mobile stations, users, terminals, mobileterminals, fixed terminals, subscriber stations, UE, user terminals, adevice, or by other terminology used in the art. The remote units 102may communicate directly with one or more of the base units 104 via ULcommunication signals.

The base units 104 may be distributed over a geographic region. Incertain embodiments, a base unit 104 may also be referred to as anaccess point, an access terminal, a base, a base station, a Node-B, aneNB, a Home Node-B, a relay node, a device, or by any other terminologyused in the art. The base units 104 are generally part of a radio accessnetwork that includes one or more controllers communicably coupled toone or more corresponding base units 104. The radio access network isgenerally communicably coupled to one or more core networks, which maybe coupled to other networks, like the Internet and public switchedtelephone networks, among other networks. These and other elements ofradio access and core networks are not illustrated but are well knowngenerally by those having ordinary skill in the art.

In one implementation, the wireless communication system 100 iscompliant with the LTE of the 3GPP protocol, wherein the base unit 104transmits using an OFDM modulation scheme on the DL and the remote units102 transmit on the UL using a SC-FDMA scheme. More generally, however,the wireless communication system 100 may implement some other open orproprietary communication protocol, for example, WiMAX, among otherprotocols. The present disclosure is not intended to be limited to theimplementation of any particular wireless communication systemarchitecture or protocol.

The base units 104 may serve a number of remote units 102 within aserving area, for example, a cell or a cell sector via a wirelesscommunication link. The base units 104 transmit DL communication signalsto serve the remote units 102 in the time, frequency, and/or spatialdomain. The unlicensed carriers 106 may be any suitable unlicensedcarrier, such as a Wi-Fi access point (“AP”). The unlicensed carriers106 may communicate with one or more of the remote units 102.

In one embodiment, a base unit 104 (e.g., device) may transmit data on acarrier to remote units 102 (e.g., set of devices) in a firsttransmission burst having a duration of at least one subframe. In suchan embodiment, the remote units 102 may include one or more remote units102. The remote unit 102 may receive the data on the carrier. Moreover,the remote unit 102 may determine an indication of whether interferenceabove a certain level exists on the carrier during the transmissionburst by comparing a received signal-to-interference-plus-noise ratio(“SINR”) in a subframe in the transmission burst with a SINR thatachieves a predetermined target block error ratio (“BLER”) for anindicated modulation and coding scheme for the data transmitted in thesubframe. Accordingly, the indication may include information that canbe used to determine whether the interference above a predeterminedlevel exists on the carrier (e.g., unlicensed carrier 106). Suchinterference may come from a hidden node or other devices operating onthe same unlicensed carrier, but the interference is not known to thebase unit 104. The remote unit 102 may transmit the indication(e.g.,feedback information) to the base unit 104. The base unit 104 mayreceive the feedback information from one or more remote units 102.Moreover, the base unit 104 may determine, based on the feedbackinformation, whether interference above a predetermined level exists onthe carrier during the first transmission burst at each device of theset of devices. The base unit 104 may also adjust a contention windowsize based on the determination of whether interference above thepredetermined level exists on the carrier during the first transmissionburst at each device of the set of devices. Moreover, the base unit 104may determine a value N between a predetermined minimum contentionwindow size and the adjusted contention window size.

FIG. 2 depicts one embodiment of an apparatus 200 that may be used forcontention window size adjustment. The apparatus 200 includes oneembodiment of the remote unit 102. Furthermore, the remote unit 102 mayinclude a processor 202, a memory 204, an input device 206, a display208, a transmitter 210, and a receiver 212. In some embodiments, theinput device 206 and the display 208 are combined into a single device,such as a touchscreen. In certain embodiments, the remote unit 102 maynot include any input device 206 and/or display 208. In variousembodiments, the remote unit 102 may include one or more of theprocessor 202, the memory 204, the transmitter 210, and the receiver212, and may not include the input device 206 and/or the display 208.

The processor 202, in one embodiment, may include any known controllercapable of executing computer-readable instructions and/or capable ofperforming logical operations. For example, the processor 202 may be amicrocontroller, a microprocessor, a central processing unit (“CPU”), agraphics processing unit (“GPU”), an auxiliary processing unit, a fieldprogrammable gate array (“FPGA”), or similar programmable controller. Insome embodiments, the processor 202 executes instructions stored in thememory 204 to perform the methods and routines described herein. Theprocessor 202 is communicatively coupled to the memory 204, the inputdevice 206, the display 208, the transmitter 210, and the receiver 212.In certain embodiments, the processor 202 may determine an indication ofwhether interference above a certain level exists on the carrier duringthe transmission burst by comparing a receivedsignal-to-interference-plus-noise ratio (“SINR”) in a subframe in thetransmission burst with a SINR that achieves a predetermined targetblock error ratio (“BLER”) for an indicated modulation and coding schemefor the data transmitted in the subframe.

The memory 204, in one embodiment, is a computer readable storagemedium. In some embodiments, the memory 204 includes volatile computerstorage media. For example, the memory 204 may include a RAM, includingdynamic RAM (“DRAM”), synchronous dynamic RAM (“SDRAM”), and/or staticRAM (“SRAM”). In some embodiments, the memory 204 includes non-volatilecomputer storage media. For example, the memory 204 may include a harddisk drive, a flash memory, or any other suitable non-volatile computerstorage device. In some embodiments, the memory 204 includes bothvolatile and non-volatile computer storage media. In some embodiments,the memory 204 stores data relating to an indication to be provided toanother device. In some embodiments, the memory 204 also stores programcode and related data, such as an operating system or other controlleralgorithms operating on the remote unit 102.

The input device 206, in one embodiment, may include any known computerinput device including a touch panel, a button, a keyboard, a stylus, amicrophone, or the like. In some embodiments, the input device 206 maybe integrated with the display 205, for example, as a touchscreen orsimilar touch-sensitive display. In some embodiments, the input device206 includes a touchscreen such that text may be input using a virtualkeyboard displayed on the touchscreen and/or by handwriting on thetouchscreen. In some embodiments, the input device 206 includes two ormore different devices, such as a keyboard and a touch panel.

The display 208, in one embodiment, may include any known electronicallycontrollable display or display device. The display 208 may be designedto output visual, audible, and/or haptic signals. In some embodiments,the display 208 includes an electronic display capable of outputtingvisual data to a user. For example, the display 208 may include, but isnot limited to, an LCD display, an LED display, an OLED display, aprojector, or similar display device capable of outputting images, text,or the like to a user. As another, non-limiting, example, the display208 may include a wearable display such as a smart watch, smart glasses,a heads-up display, or the like. Further, the display 208 may be acomponent of a smart phone, a personal digital assistant, a television,a table computer, a notebook (laptop) computer, a personal computer, avehicle dashboard, or the like.

In certain embodiments, the display 208 includes one or more speakersfor producing sound. For example, the display 208 may produce an audiblealert or notification (e.g., a beep or chime). In some embodiments, thedisplay 208 includes one or more haptic devices for producingvibrations, motion, or other haptic feedback. In some embodiments, allor portions of the display 208 may be integrated with the input device206. For example, the input device 206 and display 208 may form atouchscreen or similar touch-sensitive display. In other embodiments,the display 208 may be located near the input device 206.

The transmitter 210 is used to provide UL communication signals to thebase unit 104 and the receiver 212 is used to receive DL communicationsignals from the base unit 104. In one embodiment, the transmitter 210is used to transmit feedback information and/or an indication to thebase unit 104. In certain embodiments, the receiver 212 may be used toreceive data on a carrier in a transmission burst with a duration of atleast one subframe. Although only one transmitter 210 and one receiver212 are illustrated, the remote unit 102 may have any suitable number oftransmitters 210 and receivers 212. The transmitter 210 and the receiver212 may be any suitable type of transmitters and receivers. In oneembodiment, the transmitter 210 and the receiver 212 may be part of atransceiver.

FIG. 3 depicts another embodiment of an apparatus 300 that may be usedfor contention window size adjustment. The apparatus 300 includes oneembodiment of the base unit 104. Furthermore, the base unit 104 mayinclude a processor 302, a memory 304, an input device 306, a display308, a transmitter 310, and a receiver 312. As may be appreciated, theprocessor 302, the memory 304, the input device 306, and the display 308may be substantially similar to the processor 202, the memory 204, theinput device 206, and the display 208 of the remote unit 102,respectively. In certain embodiments, the processor 302 may be used todetermine, based on feedback information, whether interference above apredetermined level exists on a carrier during a transmission bursttransmitted to one or more remote units 102. In one embodiment, the baseunit 104 identifies the presence of interference above a predeterminedlevel for a particular remote unit 102 by examining the HARQ-ACKfeedback from the remote unit 102.

For example, assume that a remote unit 102 is scheduled with DLtransmission in M subframes in a latest transmission burst (e.g., themost recent transmission burst that the remote unit 102 received fromthe base unit 104) and provides M HARQ-ACK feedback corresponding to thePDSCH in the M scheduled subframes. In certain embodiments, the baseunit 104 identifies the presence of interference above a predeterminedlevel for the remote unit 102 if the percentage of NAKs in the MHARQ-ACK feedback from the remote unit 102 is above a certainpredetermined threshold Y, and identifies that there are no suchinterference for the remote unit 102 otherwise. In one embodiment, thevalue of the predetermined threshold Y is fixed in a specification,while in another embodiment, the value of the predetermined threshold Yis selected by the base unit 104.

In yet another embodiment, the base unit 104 identifies the presence ofinterference above a predetermined level for the remote unit 102 if theremote unit 102 feeds back NAK for more than Z consecutive scheduledsubframes, and identifies that there is no such interference for theremote unit 102 otherwise. In one embodiment, the value of the thresholdZ is fixed in a specification, while in another embodiment, the value ofthe threshold Z is selected by the base unit 104.

In another embodiment, the base unit 104 identifies the presence ofinterference above a predetermined level for a remote unit 102 byreceiving an explicit indication from the remote unit 102. In oneembodiment, the remote unit 102 sets the explicit indication of thepresence of such interference by comparing the received SINR in ascheduled subframe with the SINR used to achieve a certain target BLERfor the indicated modulation and coding scheme (“MCS”). The MCS for thePDSCH is indicated by the DL grant used for scheduling the PDSCHtransmission for a remote unit 102. In some embodiments, base unit 104selects a MCS to achieve a certain target BLER (e.g. 10% BLER). In oneembodiment, for the indicated MCS, if the received SINR calculated bythe remote unit 102 in the scheduled subframe results in a BLER higherthan the target BLER by a margin T percent, the remote unit 102 maydetermine the presence of interference above a predetermined level andthen sets the explicit indication accordingly. In one embodiment, thevalue of T is fixed in a specification. In another embodiment, the valueof T is chosen by the base unit 104.

In another embodiment, if the MCS to meet the target BLER with thereceived SINR in the scheduled subframe is S levels lower titan theindicated MCS in the DL grant, the remote unit 102 may determine thepresence of interference above a predetermined level and then sets theexplicit indication accordingly. In one embodiment, the value of S isfixed in a specification. In another embodiment, the value of S ischosen by the base unit 104 and indicated to the remote unit 102 by highlayer signaling. In another embodiment, the value of S is chosen by theremote unit 102.

In another embodiment, for a remote unit 102 scheduled with M subframesin the latest transmission burst, if the received SINRs calculated bythe remote unit 102 in each of a percentage Q of the M scheduledsubframes results in a BLER higher than the target BLER by a margin Tpercent, the remote unit 102 may determine the presence of interferenceabove a predetermined level and then sets the explicit indicationaccordingly. In yet another embodiment, for a remote unit 102 scheduledwith M subframes in the latest transmission burst, if the MCS to meetthe target BLER with the SINR in each of a percentage Q of the Mscheduled subframes is S levels lower than the indicated MCS in therespective DL grant, the remote unit 102 may determine the presence ofinterference above a predetermined level and then sets the explicitindication accordingly. In one embodiment, the value of Q is fixed in aspecification. In another embodiment, the value of Q is chosen by thebase unit 104 and indicated to the remote unit 102 by high layersignaling. In another embodiment, the value of S is chosen by the remoteunit 102.

In yet another embodiment, the base unit 104 may identify the presenceof interference above a predetermined level for a remote unit 102 byexamining the CSI feedback from the remote unit 102. The base unit 104may trigger aperiodic CSI feedback for the remote units 102 scheduled inthe latest transmission burst. In one embodiment, if the CQI feedbackcorresponding to the latest transmission burst from a remote unit 102 islower than P levels from the previous CQI feedback from the same remoteunit 102, the base unit 104 may identify the presence of interferenceabove a predetermined level for the remote unit 102; otherwise, the baseunit 104 may indicate that them is no such interference identified forthe remote unit 102. In one embodiment, the value of P is fixed by aspecification. In another embodiment, the value of P is chosen by thebase unit 104.

In some embodiments, the processor 302 may be used to adjust acontention window size based on the determination of whetherinterference above the predetermined level exists on a carrier during atransmission burst provided to one or more remote units 102 (e.g.,collectively or individually). In one embodiment the base unit 104increases the contention window size if the presence of interferenceabove a predetermined level (e.g., a hidden node problem) is identifiedfor more than a certain percentage (e.g., X) of remote units 102, anddecreases the contention window size otherwise. In one embodiment, theset of remote units 102 are the set of remote units 102 that arescheduled with DL transmission in the latest transmission burst from thebase unit 104. In one embodiment, the value of percentage X is fixed ina specification. In another embodiment, the value of percentage X ischosen by the base unit 104. In one embodiment, the base unit 104 setsthe value of percentage of X based on an assessment on how busy theunlicensed carrier is.

In one embodiment, all the scheduled remote units 102 are divided intotwo sets, Set 1 and Set 2. Set 1 includes the remote units 102 in whichthe presence of interference above a predetermined level has beenidentified and Set 2 includes the remote units 102 in which the presenceof interference above a predetermined level has not been identified. Thetwo sets may need to be updated after the completion of eachtransmission burst. In another embodiment, the base unit 104 increasesthe contention window size if it intends to schedule one or more remoteunits 102 in Set 1, in the next transmission burst. In one embodiment,the one or more UEs are scheduled with DL transmission in the latesttransmission burst from the base unit 104.

In yet another embodiment, the base unit 104 decreases the contentionwindow size if it does not intend to schedule one or more remote units102 in Set 1 in the next transmission burst. In one embodiment, the oneor more remote units 102 are scheduled with DL transmission in thelatest transmission burst from the base unit 104. In one embodimentincreasing the contention window size means doubling the contentionwindow size till the maximum value of possible contention window size.In one embodiment, decreasing the contention window size means settingthe contention window size to the minimum value of possible contentionwindow size. In certain embodiments, the processor 302 may determine avalue N between a predetermined minimum contention window size and anadjusted contention window size. In such embodiments, the value N may beused to delay a transmission burst.

The transmitter 310 is used to provide DL communication signals to theremote unit 102 and the receiver 312 is used to receive UL communicationsignals from the remote unit 102. In certain embodiments, thetransmitter 310 is used to transmit data on a carrier to one or moreremote units 102 in a first transmission burst having a duration of atleast one subframe. In one embodiment, the receiver 312 is used toreceive feedback information from the one or more remote units 102. Invarious embodiments, the transmitter 310 is used to transmit a secondtransmission burst on the carrier at least N time slots after the end ofthe first transmission burst. In such embodiments, the duration of eachtime slot may be predetermined. Although only one transmitter 310 andone receiver 312 are illustrated, the base unit 104 may have anysuitable number of transmitters 310 and receivers 312. The transmitter310 and the receiver 312 may be any suitable type of transmitters andreceivers. In one embodiment, the transmitter 310 and the receiver 312may be part of a transceiver.

FIG. 4 illustrates one embodiment of communication 400 used forcontention window size adjustment. In the illustrated embodiment, afirst remote unit 102 suffers the interference from Wi-Fi transmissions404 on an unlicensed carrier 106. However, a second remote unit 102 doesnot suffer the interference from the Wi-Fi transmissions 404 on theunlicensed carrier 106. Accordingly, the first remote unit 102 providesinterference information 406 to a base unit 104. The interferenceinformation 406 includes information that facilitates the base unit 104determining that there is a hidden node within range of the first remoteunit 102. For example, the interference information 406 may includeinformation about whether the presence of interference above apredetermined level is identified. The interference information 406 maybe any suitable information, such as HARQ-ACK feedback, CQI feedback, anactual indication of whether the first remote unit 102 detects thehidden node, and so forth.

Moreover, the second remote unit 102 provides interference information408 to the base unit 104. As may be appreciated, the interferenceinformation 408 may include information about whether the presence ofinterference above a predetermined level is identified. In theillustrated embodiment, the second remote unit 102 is not aware of thepresence of such interference, therefore, the interference information408 indicates that the second remote unit 102 has not detected suchinterference. The base unit 104 uses the information from the remoteunits 102 to determine whether there is interference above apredetermined level, and if interference is above a predetermined level,the base unit 104 may adjust a contention window size for the remoteunits 102.

FIG. 5 is a schematic flow chart diagram illustrating one embodiment ofa method 500 for contention window size adjustment. In some embodiments,the method 500 is performed by an apparatus, such as the base unit 104.In certain embodiments, the method 500 may be performed by a processorexecuting program code, for example, a microcontroller, amicroprocessor, a CPU, a GPU, an auxiliary processing unit, a FPGA, orthe like.

The method 500 may include transmitting 502 data on a carrier to a setof devices in a first transmission burst having a duration of at leastone subframe. In certain embodiments, the set of devices includes one ormote devices (e.g., remote units 102). In some embodiments, the baseunit 104 may transmit 502 the data on the carrier to the set of devicesin the first transmission burst having the duration of at least onesubframe.

The method 500 may include receiving 504 feedback information from eachdevice of the set of devices. In certain embodiments, the base unit 104may receive 504 the feedback information from each device of the set ofdevices. In some embodiments, the set of devices is scheduled for DLtransmission by the first transmission burst.

The method 500 may also include determining 506, based on the feedbackinformation, whether interference above a predetermined level exists onthe carrier during the first transmission burst at each dev ice of theset of devices. In certain embodiments, the base unit 104 maydetermining 506. based on the feedback information, whether interferenceabove the predetermined level exists on the carrier during the firsttransmission burst at each device of the set of devices.

In one embodiment, the feedback information from each device of the setof devices includes HARQ-ACK feedback corresponding to the datatransmitted in the first transmission burst to the device. In such anembodiment, determining 506, based on the feedback information, whetherinterference above the predetermined level exists on the carrier duringthe first transmission burst at each device of the set of devicesincludes determining, based on the feedback information, thatinterference above the predetermined level exists on the carrier duringthe first transmission burst for a device of the set of devices if apercentage of NAKs in the HARQ-ACK feedback from the device is greaterthan a predetermined threshold percentage. The predetermined thresholdpercentage may be any suitable percentage and may be hard coded,determined by a specification, or otherwise determined. In certainembodiments, the predetermined threshold percentage may be 10%, 15%,30%. 50%, 75%, 90%. or any other percentage.

In certain embodiments, determining 506, based on the feedbackinformation, whether interference above the predetermined level existson the carrier during the first transmission burst at each device of theset of devices includes determining, based on the feedback information,that interference above the predetermined level exists on the carrierduring the first transmission burst for a device of the set of devicesif more than a predetermined number of consecutive NAKs exist in theHARQ-ACK feedback from the device. The predetermined number ofconsecutive NAKs may be any suitable number and may be hard coded,determined by a specification, or otherwise determined. In certainembodiments, the predetermined number may be 3, 4, 5, 6, or any othersuitable number.

In various embodiments, the feedback information from each device of theset of the devices includes an indication of whether there is a hiddennode corresponding to the remote unit. For example, the indication maydefinitively indicate that either there is a hidden node, or that thereis not a hidden node detected by the remote unit. In some embodiments,the feedback information from each device of the set of devices includeschannel quality information (“CQI”) feedback from the devicecorresponding to the CQI of the device in the first transmission burst.In such embodiments, determining 506, based on the feedback information,whether interference above the predetermined level exists on the carrierduring the first transmission burst at each device of the set of devicesincludes determining, based on the feedback information, thatinterference above the predetermined level exists on the carrier duringthe first transmission burst for a device of the set of devices if theCQI feedback from the device is less than a latest CQI feedback from thedevice before the first transmission burst by a predetermined amount. Asmay be appreciated, the predetermined amount may be any suitable number.

The method 500 may include adjusting 508 a contention window size basedon the determination of whether interference above the predeterminedlevel exists on the carrier during the first transmission burst at eachdevice of the set of devices. In some embodiments, the base unit 104 mayadjust 508 the contention window size based on the determination ofwhether interference above the predetermined level exists on the carrierduring the first transmission burst at each device of the set ofdevices.

In one embodiment, adjusting 508 the contention window size includesincreasing the contention window size if interference above thepredetermined level exists on the carrier during the first transmissionburst for more than a predetermined percentage of devices in the set ofdevices. As may be appreciated, the predetermined percentage may be anysuitable percentage. Moreover, in certain embodiments, adjusting 508 thecontention window size includes decreasing the contention window size ifinterference above the predetermined level exists on the carrier duringthe first transmission burst for less than a predetermined percentage ofdevices in the set of devices. Again, the predetermined percentage maybe any suitable percentage.

In some embodiments, adjusting 508 the contention window size includesincreasing the contention window size if data is to be transmitted inthe second transmission burst to at least one device having interferenceabove the predetermined level on the carrier during the firsttransmission burst. In various embodiments, adjusting 508 the contentionwindow size includes decreasing the contention window size if data isnot to be transmitted in the second transmission burst to any devicehaving interference above the predetermined level on the carrier duringthe first transmission burst.

The method 500 may include determining 510 a value N between apredetermined minimum contention window size and the adjusted contentionwindow size. In various embodiments, the base unit 104 may determine 510the value N between the predetermined minimum contention window size andthe adjusted contention window size. As may be appreciated, thepredetermined minimum contention window size may be any suitable value,such as 1, 2, 3, and so forth. In some embodiments, the method 500 mayinclude transmitting 512 a second transmission burst on the carrier atleast N lime slots after the end of the first transmission burst. Thenthe method 500 may end. In certain embodiments, the duration of eachtime slot may be predetermined. In various embodiments, the base unit104 may transmit 512 the second transmission burst on the carrier atleast N time slots after the end of the first transmission burst.

FIG. 6 is a schematic flow chart diagram illustrating another embodimentof a method 600 for contention window size adjustment. In someembodiments, the method 600 is performed by an apparatus, such as theremote unit 102. In certain embodiments, the method 600 may be performedby a processor executing program code, for example, a microcontroller, amicroprocessor, a CPU, a GPU, an auxiliary processing unit, a FPGA, orthe like.

The method 600 may include receiving 602 data on a carrier in atransmission burst with a duration of at least one subframe. In certainembodiments, a remote unit 102 may receive 602 the data on the carrierin the transmission burst with the duration of at least one subframe.The method 600 may also include determining 604 an indication of whetherinterference above a predetermined level exists on the carrier duringthe transmission burst by comparing a received SINR in a subframe in thetransmission burst with a SINR that achieves a predetermined target BLERfor an indicated modulation and coding scheme for the data transmittedin the subframe. In one embodiment, the remote unit 102 may determinedthe indication of whether interference above the predetermined levelexists on the carrier during the transmission burst by comparing thereceived SINR in the subframe in the transmission burst with the SINRthat achieves the predetermined target BLER for the indicated modulationand coding scheme for the data transmitted in the subframe.

The method 600 may include transmitting 606 the indication to a device(e.g., a base unit 104). Then the method 600 may end. In certainembodiments, the transmitter 210 of the remote unit 102 may transmit 606the indication to the device.

Embodiments may be practiced in other specific forms. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby Ute appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

The invention claimed is:
 1. An apparatus comprising: a transmitter thattransmits data on a carrier to a set of devices in a first transmissionburst having a duration of at least one subframe, wherein the set ofdevices comprises one or more devices; a receiver that receives feedbackinformation from each device of the set of devices; and a processorthat: determines, based on the feedback information, whetherinterference above a predetermined level exists on the carrier duringthe first transmission burst at each device of the set of devices;adjusts a contention window size based on the determination of whetherinterference above the predetermined level exists on the carrier duringthe first transmission burst at each device of the set of devices; anddetermines a value N between a predetermined minimum contention windowsize and the adjusted contention window size, wherein adjusting thecontention window size comprises increasing the contention window sizeif interference above the predetermined level exists on the carrierduring the first transmission burst for more than a predeterminedpercentage of devices in the set of devices.
 2. The apparatus of claim1, wherein the transmitter transmits a second transmission burst on thecarrier at least N time slots after the end of the first transmissionburst, wherein the duration of each time slot is predetermined.
 3. Theapparatus of claim 1, wherein the feedback information from each deviceof the set of devices comprises hybrid automatic repeat requestacknowledgement (“HARQ-ACK”) feedback corresponding to the datatransmitted in the first transmission burst to the device.
 4. Theapparatus of claim 3, wherein the processor determines, based on thefeedback information, that interference above the predetermined levelexists on the carrier during the first transmission burst for a deviceof the set of devices if a percentage of negative-acknowledgments(“NAKs”) in the HARQ-ACK feedback from the device is greater than apredetermined threshold percentage.
 5. The apparatus of claim 3, whereinthe processor determines, based on the feedback information, thatinterference above the predetermined level exists on the carrier duringthe first transmission burst for a device of the set of devices if morethan a predetermined number of consecutive NAKs exist in the HARQ-ACKfeedback from the device.
 6. The apparatus of claim 1, wherein thefeedback information from each device of the set of devices compriseschannel quality information (“CQI”) feedback from the devicecorresponding to the CQI of the device in the first transmission burst.7. The apparatus of claim 6, wherein the processor determines, based onthe feedback information, that interference above the predeterminedlevel exists on the carrier during the first transmission burst for adevice of the set of devices if the CQI feedback from the device is lessthan a latest CQI feedback from the device before the first transmissionburst by a predetermined amount.
 8. The apparatus of claim 1, whereinadjusting the contention window size comprises decreasing the contentionwindow size if interference above the predetermined level exists on thecarrier during the first transmission burst for less than apredetermined percentage of devices in the set of devices.
 9. Theapparatus of claim 2, wherein adjusting the contention window sizecomprises increasing the contention window size if data is to betransmitted in the second transmission burst to at least one devicehaving interference above the predetermined level on the carrier duringthe first transmission burst.
 10. The apparatus of claim 2, whereinadjusting the contention window size comprises decreasing the contentionwindow size if data is not to be transmitted in the second transmissionburst to any device having interference above the predetermined level onthe carrier during the first transmission burst.
 11. A methodcomprising: transmitting data on a carrier to a set of devices in afirst transmission burst having a duration of at least one subframe,wherein the set of devices comprises one or more devices; receivingfeedback information from each device of the set of devices;determining, based on the feedback information, whether interferenceabove a predetermined level exists on the carrier during the firsttransmission burst at each device of the set of devices; adjusting acontention window size based on the determination of whetherinterference above the predetermined level exists on the carrier duringthe first transmission burst at each device of the set of devices; anddetermining a value N between a predetermined minimum contention windowsize and the adjusted contention window size, wherein adjusting thecontention window size comprises increasing the contention window sizeif interference above the predetermined level exists on the carrierduring the first transmission burst for more than a predeterminedpercentage of devices in the set of devices.
 12. The method of claim 11,further comprising transmitting a second transmission burst on thecarrier at least N time slots after the end of the first transmissionburst, wherein the duration of each time slot is predetermined.
 13. Themethod of claim 11, wherein the feedback information from each device ofthe set of devices comprises hybrid automatic repeat requestacknowledgement (“HARQ-ACK”) feedback corresponding to the datatransmitted in the first transmission burst to the device.
 14. Themethod of claim 13, wherein determining, based on the feedbackinformation, whether interference above the predetermined level existson the carrier during the first transmission burst at each device of theset of devices comprises determining, based on the feedback information,that interference above the predetermined level exists on the carrierduring the first transmission burst for a device of the set of devicesif a percentage of negative-acknowledgments (“NAKs”) in the HARQ-ACKfeedback from the device is greater than a predetermined thresholdpercentage.
 15. The method of claim 13, wherein determining, based onthe feedback information, whether interference above the predeterminedlevel exists on the carrier during the first transmission burst at eachdevice of the set of devices comprises determining, based on thefeedback information, that interference above the predetermined levelexists on the carrier during the first transmission burst for a deviceof the set of devices if more than a predetermined number of consecutiveNAKs exist in the HARQ-ACK feedback from the device.
 16. The method ofclaim 11, wherein the feedback information from each device of the setof devices comprises channel quality information (“CQI”) feedback fromthe device corresponding to the CQI of the device in the firsttransmission burst.
 17. The method of claim 16, wherein determining,based on the feedback information, whether interference above thepredetermined level exists on the carrier during the first transmissionburst at each device of the set of devices comprises determining, basedon the feedback information, that interference above the predeterminedlevel exists on the carrier during the first transmission burst for adevice of the set of devices if the CQI feedback from the device is lessthan a latest CQI feedback from the device before the first transmissionburst by a predetermined amount.